Tuning the Electronic and Optical Properties of Phenoxaborin Based Thermally Activated Delayed Fluorescent Materials: A DFT Study.

The electronic and optoelectronic properties of molecules constituted by benzene as linker, phenoxaborin as acceptor coupled with different types of donor moieties are investigated using the density functional theoretical method. The energy gap between the first excited singlet and triplet states (ΔEST) of the designed molecules (1-9) is found to be less than 0.5 eV suggesting them as ideal candidates for thermally activated delayed fluorescence (TADF) emitters. The analysis of frontier molecular orbitals of the molecules revealed a minimum spatial overlap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in favor of the small values of ΔEST. Among the molecules studied, the one in which dihydrophenazine acts as the donor has the lowest value of ΔEST. All designed molecules are good electron transporters. The non-linear optical properties of the molecules are also examined.

Water-assisted absorption of CO2 by 3-amino-1-propanol: a mechanistic insight.

The mechanism of the proton transfer in the reaction between CO2 and 3-amino-1-propanol with and without water molecules is investigated quantum-mechanically. Studies revealed that water molecules and the hydroxy group of 3-amino-1-propanol explicitly participate in the proton transfer, forming carbamic acid. It is found that water has a high impact on the energetics of CO2 absorption by reducing the barrier for proton transfer. Apart from the water molecules, the hydroxy group of alkanolamine significantly affects the energetics of the reaction. Five cases involving two, three, and four protons are discussed, and it is found that the proton transfer occurs in a concerted manner that depends on the initial configuration of the reaction complex. The present study unequivocally confirms the role of water molecules in the CO2 capturing via amine-based solvents.

Effect of Electron-Donating Substituents and an Electric Field on the ΔEST of Selected Imidazopyridine Derivatives: A DFT Study.

A series of thermally activated delayed fluorescent (TADF) molecules having an imidazopyridine acceptor, a benzene linker, and a 9,9-dimethyl-9,10-dihydroacridine donor are designed and examined using a quantum chemical approach. The above framework spatially separates the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), minimizing their overlap, ultimately resulting in a reduced energy gap between the excited singlet and triplet states (ΔEST). The impact of electron-donating substituents (-Me, -Et, -t-Bu, -OMe, and -NMe2) on the donor moiety of the parent molecule 2-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)imidazo[1,2-a]pyridine-3,6-dicarbonitrile (Ac-CNImPy) is investigated. The calculated results revealed that for a given substituent, the para-substituted derivatives exhibit relatively less ΔEST, compared to that of the respective ortho- and meta derivatives. The value of ΔEST decreased with an increase in the electron-donating capacity of the substituent. Additionally, the ΔEST of the disubstituted derivatives is found to be less than that for the monosubstituted derivatives. The charge transport studies revealed that molecules with strong electron-donating substituents act as electron transporters. The effect of an external electric field (EEF) on ΔEST of the parent molecule Ac-CNIMPY and its derivative is also examined and revealed that the ΔEST can be further reduced by applying an electric field of appropriate strength in a direction perpendicular to the dipole moment of the molecule and in the plane of the acceptor moiety.

Spontaneous Curvature Induction in an Artificial Bilayer Membrane.

Maintaining lipid asymmetry across membrane leaflets is critical for functions like vesicular traffic and organelle homeostasis. However, a lack of molecular-level understanding of the mechanisms underlying membrane fission and fusion processes in synthetic systems precludes their development as artificial analogs. Here, we report asymmetry induction of a bilayer membrane formed by an extended π-conjugated molecule with oxyalkylene side chains bearing terminal tertiary amine moieties (BA1) in water. Autogenous protonation of the tertiary amines in the periphery of the bilayer by water induces anisotropic curvature, resulting in membrane fission to form vesicles and can be monitored using time-dependent spectroscopy and microscopy. Interestingly, upon loss of the induced asymmetry by extensive protonation using an organic acid restored bilayer membrane. The mechanism leading to the compositional asymmetry in the leaflet and curvature induction in the membrane is validated by density functional theory (DFT) calculations. Studies extended to control molecules having changes in hydrophilic (BA2) and hydrophobic (BA3) segments provide insight into the delicate nature of molecular scale interactions in the dynamic transformation of supramolecular structures. The synergic effect of hydrophobic interaction and the hydrated state of BA1 aggregates provide dynamicity and unusual stability. Our study unveils mechanistic insight into the dynamic transformation of bilayer membranes into vesicles.

Tuning of the Singlet-Triplet Energy Gap of Donor-Linker-Acceptor Based Thermally Activated Delayed Fluorescent Emitters.

Thermally activated delayed fluorescent emitters based on carbazole donor, benzonitrile acceptor with the linkers biphenyl, bipyridine and naphthalene are investigated using the density functional theoretical method. The molecule in which bipyridine acts as the linker with the least ΔEST is further selected for the designing of a series of D-L-A framework TADF molecules. Remarkably, the ΔEST is decreased successively by attaching the additional cyano groups at the acceptor site which is further reduced when the electron donating methoxy groups are attached at the donor site. To know the effect of substituents on ΔEST, the acceptor moiety of the D-L-A framework is modified with -F, -Cl and -CF3 substituents. The studies showed a relatively less decrement in the value of ΔEST compared to the cyano substituted molecules. However, ΔEST significantly reduced further on attaching methoxy groups at the donor site.

Probing the Interaction of NO with C60: Comparison between Endohedral and Exohedral Complexes.

Recent advances in synthetic methodologies have opened new strategies for synthesizing stable metal-free electron spin systems based on fullerenes. Introducing nitric oxide (NO) inside a fullerene cage is one of the methods to attain this goal. In the present study, dispersion corrected density functional theory (B3LYP-D3) has been used to evaluate the structure, stability, and electronic properties of NO encapsulated fullerene NO@C60 and compared those with its exohedral fullerene NO.C60 analog. The calculated stabilization energy for NO@C60 is appreciably higher than NO.C60, and this difference is comprehended via the Quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) topological analyses. The delocalization of electron density of NO and the C60 cage in NO@C60 is discussed using electrostatic potential analysis. In addition, an attempt has been made to understand the different locations and orientations involving the interaction of two NO radicals and the fullerene C60. It is shown that the encapsulation of the NO dimer inside the C60 cage is an energetically unfavorable process. On the other hand, stable structures are obtained upon the physisorption of other NO on the surface of NO@C60 and NO.C60. The present work provides an in-depth understanding of the interaction of NO and C60 fullerene, its preferable position, and its orientation in both endohedral and exohedral complexes.

Nitrogen Amelioration-Driven Carbon Dioxide Capture by Nanoporous Polytriazine.

Nitrogen-enriched nanoporous polytriazines (NENPs) have been synthesized by ultrafast microwave-assisted condensation of melamine and cyanuric chloride. The experimental conditions have been optimized to tune the textural properties by synthesizing materials at different times, temperatures, microwave powers, and solvent contents. The maximum specific surface area (SABET) of 840 m2 g-1 was estimated in the sample (NENP-1) synthesized at 140 °C with a microwave power of 400 W and reaction time of 30 min. One of the major objectives of achieving a large nitrogen content as high as 52 wt % in the framework was realized. As predicted, the nitrogen amelioration has benefitted the application by capturing a very good amount of CO2 of 22.9 wt % at 273 K and 1 bar. Moreover, the CO2 storage capacity per unit specific surface area (per m2 g-1) is highest among the reported nanoporous organic frameworks. The interaction of the CO2 molecules with the polytriazine framework was theoretically investigated by using density functional theory. The experimental CO2 capture capacity was validated from the outcome of the theoretical calculations. The superior CO2 capture capability along with the theoretical investigation not only makes the nanoporous NENPs superior adsorbents for the energy and environmental applications but also provides a significant insight into the fundamental understanding of the interaction of CO2 molecules with the amine functionalities of the nanoporous frameworks.

Spin density transfer from guest to host in endohedral heterofullerene dimers.

The endohedral heterofullerenes (B@C59B)2, (B@C59N)2, (N@C59B)2 and (B@C59N-N@C59B) are investigated using dispersion corrected density functional theory. Several spin states of these complexes are considered and their stable spin states are reported. For 1[(B@C59B)2] and 1[(B@C59N-N@C59B)], the encapsulated atoms are positioned near the surface of the host cages, in contrast to other spin states where they are positioned at the centre of the cages. In complexes 1[(B@C59N)2], 3[(B@C59N)2] and 7[(N@C59B)2], the guest atoms are found to be at the centre of the host cages. The spin polarization and the transfer of spin density between the components of the complexes for different stable spin states are analyzed. Based on the spin states of the complexes, the spin-spin interaction is found to be either ferromagnetic or anti-ferromagnetic. Unlike other complexes, in 1[(B@C59B)2] and 1[(B@C59N-N@C59B)] the spin density is transferred from the guest to the host followed by anti-ferromagnetic coupling between the monomers. The thermodynamic feasibility of formation of the complexes is also examined. The electron affinity, ionization potential and dipole moment of the above systems are determined. The singlet state of the heterodimer (B@C59N-N@C59B) showed high polarity due to the slight rotation along the dihedral angle φNCCB.

Switching the charge transfer characteristics of quaterthiophene from p-type to n-type via interactions with carbon nanotubes.

Carbon nanotube-based semiconductors are of great interest for optoelectronic applications at the nanoscale. The present study investigates the structural, optoelectronic and charge transport properties of non-covalent complexes formed between carbon nanotubes (CNTs) and quaterthiophene (4T) by employing dispersion-corrected density functional methods. The effect of different functionals viz., B97-D, B3LYP-GD3 and ωB97X-D on the properties of endo- and exohedral complexes is examined. The endohedral complex (4T@CNT) is found to be energetically more stable than the exohedral one (4T-CNT). Electronic properties such as the ionization energy, electron affinity and energy gap between the frontier molecular orbitals of the CNT are not significantly changed by the adsorption or the encapsulation of 4T. Contrary to the p-type characteristics of 4T, its complexes formed with CNTs exhibit n-type characteristics due to the higher electron mobility than the hole mobility. Among the endo- and exohedral complexes, the former one shows the highest electron mobility of 3.79 cm2 V-1 s-1. The absorption properties of all the systems were studied by time-dependent density functional theory (TD-DFT). It is found that the complexes undergo several charge transfer transitions in the visible region of the electromagnetic spectrum. The above results unequivocally suggest that the charge-transfer characteristics of 4T can be altered on forming complexes with CNTs.

Structural, optoelectronic and charge transport properties of the complexes of indigo encapsulated in carbon nanotubes.

Using the dispersion-corrected density functional B97D and 6-31g(d,p) basis set, the structural, stability, electronic, optical and charge transport properties of the complexes formed by encapsulating indigo inside carbon nanotubes (CNTs) of varying diameters are investigated. Based on the stabilization energy of the complexes indigo@(n,n)CNT (where n = 6, 7 and 8), indigo@(7,7)CNT is shown to be the most stable owing to the ideal diameter of (7,7)CNT for encapsulating indigo. The nature of the interaction between the guest and the host is investigated by means of energy decomposition analysis employing the symmetry adapted perturbation theory. Electronic properties such as the ionization energy, the electron affinity and the energy gap between the highest occupied and lowest unoccupied molecular orbitals (ΔEH-L) of the complexes are determined. The low values of ΔEH-L (<1 eV) for the complexes suggest that they can act as narrow energy gap semiconductors. All the complexes exhibit high hole and electron mobilities which vary inversely with respect to the diameter of the CNT. Using the time-dependent density functional theoretical method, the absorption properties are predicted for the most stable complex indigo@(7,7)CNT. The presence of charge transfer peaks in the visible and near-infrared regions of the electromagnetic spectrum suggests that the complexes are suitable for optoelectronic devices such as solar cells.

Formation of a nanobubble and its effect on the structural ordering of water in a CH4-N2-CO2-H2O mixture.

The replacement of methane (CH4) from its hydrate by a mixture of nitrogen (N2) and carbon dioxide (CO2) involves the dissociation of methane hydrate leading to the formation of a CH4-N2-CO2-H2O mixture that can significantly influence the subsequent steps of the replacement process. In the present work, we study the evolution of dissolved gas molecules in this mixture by applying classical molecular dynamics simulations. Our study shows that a higher CO2 : N2 ratio in the mixture enhances the formation of nanobubbles composed of N2, CH4 and CO2 molecules. To understand how the CO2 : N2 ratio affects nanobubble nucleation, the distribution of molecules in the bubble formed is examined. It is observed that unlike N2 and CH4, the density of CO2 in the bubble reaches a maximum at the surface of the bubble. The accumulation of CO2 molecules at the surface makes the bubble more stable by decreasing the excess pressure inside the bubble as well as surface tension at its interface with water. It is found that a frequent exchange of gas molecules takes place between the bubble and the surrounding liquid and an increase in concentration of CO2 in the mixture leads to a decrease in the number of such exchanges. The effect of nanobubbles on the structural ordering of water molecules is examined by determining the number of water rings formed per unit volume in the mixture. The role of nanobubbles in water structuring is correlated to the dynamic nature of the bubble arising from the exchange of gas molecules between the bubble and the liquid.

Structure, Stability, and Properties of Boron Encapsulated Complexes of C60, C59B, and C59N.

Density functional studies are performed for the boron atom encapsulated complexes of C60, C59B, and C59N using B3LYP and B3LYP-GD2 functionals with 6-311G* basis set. The study shows that the complexes B@C59B and B@C59N can exist in different forms which differ in their structure as well as electronic and magnetic properties. The nature of interaction between the guest and the host is analyzed based on the stabilization energies of complexes for their different spin states. The electronic properties such as vertical electron affinity (VEA), vertical ionization energy (VIE), and energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the complexes are calculated. The transfer of electron spin density and spin-spin coupling of electrons between the guest and the host are examined. The study reveals that ferromagnetic core@shell spin coupling occurs between the host and the guest species of the complexes B@C59B and B@C59N in their triplet state without any transfer of spin density. The values of hyperfine coupling constant (hfcc) for the heteroatom of the cage and for the encapsulated boron atom of the complexes are analyzed, and it indicates that the value of hfcc for the encapsulated boron decreases significantly due to confinement.

Charge transport and optical properties of the complexes of indigo wrapped over carbon nanotubes.

A new molecular system comprising the non-covalently functionalized complexes of single walled (6,6) carbon nanotubes (SWCNTs) of finite length with indigo is proposed based on the dispersion-corrected density functional theory calculations. In the complexes viz. the dyad and triad, indigo is wrapped over carbon nanotubes in the ratio of 1 : 1 and 2 : 1, respectively. A comprehensive study of stabilization energy, ionization energy, electron affinity, the energy gap between the highest occupied and lowest unoccupied molecular orbitals (ΔELUMO-HOMO), and absorption spectra unravels the structure-property relationship of the complexes. The energy gap of ∼1 eV between the HOMO and the LUMO of the complexes suggests that they can be semiconductive. The energy levels of the frontier molecular orbitals of indigo and CNT suggest the possibility of the photoinduced charge transfer between them. Using the charge hopping rate based on Marcus theory, a hole mobility as high as 8.77 cm(2) V(-1) s(-1) is obtained for the dyad. For both the dyad and triad, a higher value of hole mobility than electron mobility is observed, thereby suggesting them to be useful for p-type semiconductor devices. The time-dependent density functional theory (TD-DFT) calculations predict that the absorption of indigo-CNT complexes occurs in the visible and the near-infrared regions finding applications in organic light emitting diodes (OLEDs). Furthermore, the effects of the length and the capping of CNTs as well as the orientation of indigo over the CNTs on the charge transport properties are also discussed.

Carbon dioxide induced bubble formation in a CH4-CO2-H2O ternary system: a molecular dynamics simulation study.

The extraction of methane from its hydrates using carbon dioxide involves the decomposition of the hydrate resulting in a CH4-CO2-H2O ternary solution. Using classical molecular dynamics simulations, we investigate the evolution of dissolved gas molecules in the ternary system at different concentrations of CO2. Various compositions considered in the present study resemble the solution formed during the decomposition of methane hydrates at the initial stages of the extraction process. We find that the presence of CO2 aids the formation of CH4 bubbles by causing its early nucleation. Elucidation of the composition of the bubble revealed that in ternary solutions with high concentration of CO2, mixed gas bubbles composed of CO2 and CH4 are formed. To understand the role of CO2 in the nucleation of CH4 bubbles, the structure of the bubble formed was analyzed, which revealed that there is an accumulation of CO2 at the interface of the bubble and the surrounding water. The aggregation of CO2 at the bubble-water interface occurs predominantly when the concentration of CO2 is high. Radial distribution function for the CH4-CO2 pair indicates that there is an increasingly favorable direct contact between dissolved CH4 and CO2 molecules in the bubble-water interface. It is also observed that the presence of CO2 at the interface results in the decrease in surface tension. Thus, CO2 leads to greater stability of the bubble-water interface thereby bringing down the critical size of the bubble nuclei. The results suggest that a rise in concentration of CO2 helps in the removal of dissolved CH4 thereby preventing the accumulation of methane in the liquid phase. Thus, the presence of CO2 is predicted to assist the decomposition of methane hydrates in the initial stages of the replacement process.

Spin-Spin Coupling in Nitrogen Atom Encapsulated C60, C59N, and Their Respective Dimers.

Density functional theoretical calculations were performed to study the stability and magnetic properties of nitrogen-encapsulated C60, C59N, and their respective dimers at B3LYP/6-311G* and B3LYP-GD2/6-311G* levels of theory. For the most stable spin state of each of the above complexes, spin density transfer and spin-spin coupling between different components are investigated. The nature of bonding between the guest and the host is analyzed based on the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap and the respective molecular orbital diagrams. The analysis of spin density showed that the encapsulated nitrogen retained its atomic state in N@C60 and N@C59N. Depending on the multiplicity of N@C59N, the unpaired electrons of the encapsulated nitrogen are coupled with those of the cage anti-ferromagnetically or ferromagnetically. The present study also showed that the complex (N@C60)2 can exist in two isoenergetic spin states, namely, (7)[(N@C60)2] and (1)[(N@C60)2]. In the former, the encapsulated nitrogens are ferromagnetically coupled, whereas they are coupled anti-ferromagnetically in the latter. A similar coupling between the guest species occurs in the nitrogen analogues (7)[(N@C59N)2] and (1)[(N@C59N)2]. The stabilization energy of the endohedral nitrogen complexes indicated that the interaction between the guest and the host cage is purely noncovalent.

Structure and properties of small aurocarbons: a selective study.

Gold clusters are versatile catalysts, and adding nonmetal dopants can allow tuning of their electronic properties via both shape and composition alteration. In the present work, mixed clusters of carbon and gold atoms are studied in terms of structure, stability, and the correlation between the shape and electronic properties by using a density functional theory approach. Four series of isomers (hydrocarbon analogues, carbon chains and cycles on gold surface, and carbon cores encapsulated by gold atoms) are investigated, exhibiting variation of the relative stability with the system size. Calculated vertical ionization energies, vertical electron affinities, and HOMO-LUMO energy gaps of the mixed clusters show a considerable change relative to the values for the pure gold clusters, the properties generally altering more strongly for the gold-encapsulated-carbon isomers. Also discussed are the structure, stability, and properties of larger clusters with a few such encapsulated-carbon units, with pronounced effects due to aggregation.

Protective and restorative effects of a Commiphora mukul gum resin and triheptanoin preparation on the CCL-110 skin fibroblast cell line.

Coenzyme Q10 (CoQ10) is a major ingredient in skin care products because of its anti-wrinkle effects, although it has some side effects especially at higher amounts. In this study, we compare the anti-wrinkle related properties of CoQ10 and a proprietary Commiphora mukul gum resin (guggul) and triheptanoin preparation (GU-TC7). GU-TC7 is prepared with a supercritical CO2-co-solvent extraction with ethanol, standardized to 2% guggulsterones and triheptanoin, a triglyceride composed of three 7-carbon fatty acids. Treatment of CCL-110 skin fibroblasts with GU-TC7 demonstrates a mild proliferative effect compared to CoQ10 and increased type I collagen synthesis. Additionally, GU-TC7 inhibited matrix metalloproteinase-1 (MMP-1) expression in a dose-dependent manner at 20-100 µg mL⁻¹ and inhibited human elastase expression by more than 50% as compared to no elastase inhibition with CoQ10 treatment. These results suggest that GU-TC7 possesses properties that are applicable to the treatment of wrinkles and may be considered for its further evaluation in skin care products.

Rho-Rho kinase pathway in the actomyosin contraction and cell-matrix adhesion in immortalized human trabecular meshwork cells.

PURPOSE: The outflow facility for aqueous humor across the trabecular meshwork (TM) is enhanced by agents that oppose the actomyosin contraction of its resident cells. Phosphorylation of MYPT1 (myosin light chain [MLC] phosphatase complex of Type 1) at Thr853 and Thr696 inhibits dephosphorylation of MLC, leading to an increase in actomyosin contraction. In this study, we examined the effects of Rho kinase (ROCK) inhibitors on the relative dephosphorylation of the two sites of MYPT1 using human TM cells (GTM3). METHODS: Dephosphorylation of MYPT1 at Thr853 and Thr696 was determined by western blot analysis following exposure to selective inhibitors of ROCK, namely Y-27632 and Y-39983. Consequent dephosphorylation of MLC and decreases in actomyosin contraction were assessed by western blot analysis and collagen gel contraction assay, respectively. Changes in the cell-matrix adhesion were measured in real time by electric cell-substrate impedance sensing and also assessed by staining for paxillin, vinculin, and focal adhesion kinase (FAK). RESULTS: Both ROCK inhibitors produced a concentration-dependent dephosphorylation at Thr853 and Thr696 of MYPT1 in adherent GTM3 cells. IC50 values for Y-39983 were 15 nM and 177 nM for dephosphorylation at Thr853 and Thr696, respectively. Corresponding values for Y-27632 were 658 nM and 2270 nM. Analysis of the same samples showed a decrease in MLC phosphorylation with IC50 values of 14 nM and 1065 nM for Y-39983 and Y-27632, respectively. Consistent with these changes, both inhibitors opposed contraction of collagen gels induced by TM cells. Exposure of cells to the inhibitors led to a decrease in the electrical cell-substrate resistance, with the effect of Y-39983 being more pronounced than Y-27632. Treatment with these ROCK inhibitors also showed a loss of stress fibers and a concomitant decrease in tyrosine phosphorylation of paxillin and FAK. CONCLUSIONS: Y-39983 and Y-27632 oppose ROCK-dependent phosphorylation of MYPT1 predominantly at Thr853 with a corresponding decrease in MLC phosphorylation. A relatively low effect of both ROCK inhibitors at Thr696 suggests a role for other Ser/Thr kinases at this site. Y-39983 was several-fold more potent when compared with Y-27632 at inhibiting the phosphorylation of MYPT1 at either Thr853 or Thr696 commensurate with its greater potency at inhibiting the activity of human ROCK-I and ROCK-II enzymes.

Increased insulin sensitivity and obesity resistance in mice lacking the protein tyrosine phosphatase-1B gene.

Protein tyrosine phosphatase-1B (PTP-1B) has been implicated in the negative regulation of insulin signaling. Disruption of the mouse homolog of the gene encoding PTP-1B yielded healthy mice that, in the fed state, had blood glucose concentrations that were slightly lower and concentrations of circulating insulin that were one-half those of their PTP-1B+/+ littermates. The enhanced insulin sensitivity of the PTP-1B-/- mice was also evident in glucose and insulin tolerance tests. The PTP-1B-/- mice showed increased phosphorylation of the insulin receptor in liver and muscle tissue after insulin injection in comparison to PTP-1B+/+ mice. On a high-fat diet, the PTP-1B-/- and PTP-1B+/- mice were resistant to weight gain and remained insulin sensitive, whereas the PTP-1B+/+ mice rapidly gained weight and became insulin resistant. These results demonstrate that PTP-1B has a major role in modulating both insulin sensitivity and fuel metabolism, thereby establishing it as a potential therapeutic target in the treatment of type 2 diabetes and obesity.

A multifunctional triazine-based nanoporous polymer as a versatile organocatalyst for CO2 utilization and C-C bond formation.

A triazine-based nanoporous multifunctional polymer with a SABET of 304 m2 g-1 has shown versatile catalytic activity in the conversion of CO2 to cyclic carbonates at 4 bar with almost 100% yield and selectivity, and in the conversion of CO2 to methanol and methane electrochemically. Additionally, it also catalyzes C-C bond formation via the Knoevenagel reaction.